Jeffrey Panko NP Psychiatry · Patient education
Diphenhydramine
Benadryl / Some OTC allergy and sleep formulations
A guide for adults taking diphenhydramine.
Follow the directions on your prescription and your provider's recommendations.
Formulations: Tablets, capsules, dissolving formulations, liquids, and combination medicines have different ingredients and strengths. Read the active-ingredient list to avoid duplicate diphenhydramine.
What it is used for
Diphenhydramine treats allergy symptoms and is included in some over-the-counter sleep aids. It is generally a poor choice for ongoing insomnia because of next-day effects, tolerance to sedation, and anticholinergic risks.
How it works
It blocks histamine H1 receptors, which reduces allergy symptoms and causes sleepiness. It also blocks acetylcholine, contributing to dry mouth, constipation, urinary problems, and confusion.
What to expect over time
Sedation can occur after a dose, but the sleep effect may weaken with repeated use. Persistent insomnia needs assessment rather than a higher dose.
Taking your medication
- Use only the labeled or prescribed amount. Do not combine oral and topical diphenhydramine without review.
- Avoid alcohol and other sleep aids.
- Do not take a late catch-up dose for sleep or double a missed dose.
- Do not use it to make a child sleepy.
When to get help
Emergency symptoms. Get emergency care for a seizure, collapse, severe confusion or hallucinations, a fast irregular heartbeat, or trouble breathing. An overdose can be life-threatening.
Prompt medical advice. Report inability to urinate, painful red eyes with visual changes, persistent confusion, or repeated falls.
If you feel unsafe or have thoughts of self-harm, call 911 or go to an emergency department.
Possible side effects
- Drowsiness, slowed reactions, or dizziness
- Dry mouth, constipation, or blurred vision
- Difficulty urinating
- Confusion or, occasionally, agitation
Keeping track of treatment
Some side effects resolve with time; others may require a change of medication. Discuss persistent or bothersome side effects with your provider.
Watch for next-day impairment, falls, constipation, and mental confusion. Older adults are especially vulnerable to these effects.
If you take too much
For a suspected overdose, call Poison Control at 1-800-222-1222 immediately, even if you feel well. Call 911 for a seizure, collapse, trouble breathing, or inability to wake.
Before you start
Discuss glaucoma, urinary retention or prostate problems, severe constipation, breathing disease, and memory concerns. Older adults should review alternatives with their provider.
Discuss pregnancy, pregnancy plans, and breastfeeding with your provider. Treatment decisions should consider both the medication and the condition being treated.
Medicines and interactions
Review all your medications with your provider, including over-the-counter medicines and supplements. Have new medications checked before taking them.
Alcohol, opioids, benzodiazepines, and other sedatives can add dangerous impairment. Other anticholinergics increase confusion, constipation, and urinary retention.
Many nighttime cold, pain, and allergy medicines already contain a sedating antihistamine. Review all ingredients.
Everyday tips
Check “PM” and combination medicine labels before every new purchase.
Avoid driving while drowsy or visually impaired.
Your questions answered
Is an OTC sleep aid harmless?
No. Nonprescription availability does not remove effects on alertness, memory, heart rhythm, or overdose risk.
What can help ongoing insomnia?
Consult with your provider about the cause and CBT-I. Adding more diphenhydramine is not a good long-term strategy.
Storage and safety
Keep medication in its labeled container, away from excess heat and moisture and out of reach of children and pets. Do not share it. Ask a pharmacy about disposal of unused medication.
Sources
About this information
Educational handout; does not replace your prescription or provider's recommendations.
Educational inclusion does not mean this medication or its indications are treated at this practice. Review the guide for your exact product with your prescriber or pharmacist.